The following pseudo code

Func out0, out1;
out0(x,y) = 1 * in(x,y);
out1(x,y) = 2 * in(x,y);

out0.vectorize(x, vs);
out1.vectorize(x, vs).compute_with(out0, x);

out0.specialize(in.dim(1).stride() == 128).fuse(x,y,f);

will generate code where out1 is never written for the specialized case, only out0 is.
This should instead either give a generation time error or ideally fuse the compute_with function(s) as well.